Michael Johnson was convicted this month of second-degree murder in the death of 16-year-old Phylicia Barnes, an honor student who disappeared while visiting relatives in Baltimore in December 2010. Her body was found four months later in the Susquehanna River.

Johnson's lawyers filed a motion for a new trial on Tuesday. Attorney Russell Neverdon says prosecutors improperly tried to bolster the credibility of a witness who testified that Johnson asked him for help disposing of Barnes' body.

Baltimore State's Attorney Gregg Bernstein says the state will respond to the motion at the appropriate time.

Johnson's sentencing is scheduled for March 20. He faces up to 30 years in prison.